package edu.princeton.cs.algs4;

import edu.princeton.cs.stdlib.In;
import edu.princeton.cs.stdlib.StdOut;

/*************************************************************************
 * Compilation: javac DepthFirstPaths.java Execution: java DepthFirstPaths G s
 * Dependencies: Graph.java Stack.java
 * 
 * Run depth first search on an undirected graph. Runs in O(E + V) time.
 * 
 * % java Graph tinyCG.txt 6 8 0: 2 1 5 1: 0 2 2: 0 1 3 4 3: 5 4 2 4: 3 2 5: 3 0
 * 
 * % java DepthFirstPaths tinyCG.txt 0 0 to 0: 0 0 to 1: 0-2-1 0 to 2: 0-2 0 to
 * 3: 0-2-3 0 to 4: 0-2-3-4 0 to 5: 0-2-3-5
 * 
 *************************************************************************/

public class DepthFirstPaths {
	private boolean[] marked; // marked[v] = is there an s-v path?
	private int[] edgeTo; // edgeTo[v] = last edge on s-v path
	private final int s; // source vertex

	public DepthFirstPaths(Graph G, int s) {
		this.s = s;
		edgeTo = new int[G.V()];
		marked = new boolean[G.V()];
		dfs(G, s);
	}

	// depth first search from v
	private void dfs(Graph G, int v) {
		marked[v] = true;
		for (int w : G.adj(v)) {
			if (!marked[w]) {
				edgeTo[w] = v;
				dfs(G, w);
			}
		}
	}

	// is there a path between s and v?
	public boolean hasPathTo(int v) {
		return marked[v];
	}

	// return a path between s to v; null if no such path
	public Iterable<Integer> pathTo(int v) {
		if (!hasPathTo(v))
			return null;
		Stack<Integer> path = new Stack<Integer>();
		for (int x = v; x != s; x = edgeTo[x])
			path.push(x);
		path.push(s);
		return path;
	}

	public static void main(String[] args) {
		In in = new In(args[0]);
		Graph G = new Graph(in);
		// StdOut.println(G);

		int s = Integer.parseInt(args[1]);
		DepthFirstPaths dfs = new DepthFirstPaths(G, s);

		for (int v = 0; v < G.V(); v++) {
			if (dfs.hasPathTo(v)) {
				StdOut.printf("%d to %d:  ", s, v);
				for (int x : dfs.pathTo(v)) {
					if (x == s)
						StdOut.print(x);
					else
						StdOut.print("-" + x);
				}
				StdOut.println();
			}

			else {
				StdOut.printf("%d to %d:  not connected\n", s, v);
			}

		}
	}

}
